1. Field of the Invention
The present invention relates to a receiver with a sigma-delta structure that can applied to a WPAN communication system, such as Zigbee, and more particularly, to a receiver with a sigma-delta structure that can perform signal amplification and RSSI calculation according to power of an output signal of a mixer without using an automatic gain controller (AGC) in a configuration using a sigma-delta A/D converter.
2. Description of the Related Art
In general, a receiver that can be applied to a wireless personal area network (WPAN) communication system, such as Zigbee, includes a low noise amplifier (LNA), a mixer, a programmable gain amplifier (PGA), a automatic gain controller (AGC), a band pass filter (BPF), and the like. However, the general receiver has lower adaptability to a communication environment, for example, low current consumption.
An RF receiver has been gradually digitalized. The digitalized receiver may use a sigma-delta A/D converter as an A/D converter.
However, when the sigma-delta A/D converter is used by a method according to the related art, a receiver uses a received signal strength indicator (RSSI) that indicates sensitivity of a received signal and an existing AGC. For this reason, the receiver is limited in terms of current consumption and area when digitalizing the receiver.
FIG. 1 is a configuration view illustrating a receiver according to the related art that uses a general A/D converter.
As shown in FIG. 1, a receiver according to the related art includes a low noise amplifier 11, a mixer 12, a filter 13, a PGA 14, an A/D converter 15, and a demodulator 16. The low noise amplifier 11 amplifies a signal from an antenna ANT. The mixer 12 converts an RF signal from the low noise amplifier 11 into an IF signal. The filter 13 passes the IF signal from the mixer 12. The PGA 14 controls power of the IF signal from the filter 13. The A/D converter 15 converts an analog signal from the PGA 14 into a digital signal. The demodulator 16 automatically controls the gain of the PGA 14 and demodulates the signal from the A/D converter 15.
The demodulator 16 of the receiver according to the related art can calculate power of a received signal by the following Equation 1.(Power)=(SI−offset)2+(SQ−offset)2  [Equation 1]
Here, offset is an intermediate value of the output signal of the A/D converter 15.
The demodulator 16 calculates the power of the received signal by the above Equation 1 and controls the gain of the PGA 14 according to the power, so that a signal having an appropriate level is supplied to the A/D converter 15.
In the receiver according to the related art, shown in FIG. 1, a constant value always needs to be input to the A/D converter 15. To this end, a PGA is used.
However, since the A/D converter has a narrow input range, the A/D converter is limited when processing a received signal. To overcome this, a sigma-delta A/D converter that has advantages in terms of area and current consumption may be directly applied to the receiver according to the related art, shown in FIG. 1, to use the PGA, which undermines the advantages of the sigma-delta A/D converter. Accordingly, there is a need for a receiver adaptive to the sigma-delta A/D converter.
FIG. 2 is a configuration view illustrating a receiver with a sigma-delta A/D converter according to the related art.
A receiver with a sigma-delta A/D converter according to the related art, shown in FIG. 2, includes an RF unit 21, a filter 22, an AGC 23, a sigma-delta A/D converter 24, and a demodulator 25. The RF unit 21 converts an RF signal from an antenna ANT into an IF signal. The filter 22 passes the IF signal from the RF unit 21. The AGC 23 amplifies the signal form the filter 22 according to automatic gain control. The sigma-delta A/D converter 24 converts the signal from the AGC 23 into a digital signal according to a sigma-delta conversion method. The modulator 25 detects RSSI (received signal strength indication) with respect to the digital signal from the sigma-delta A/D converter 24 and automatically controls the gain of the AGC 23.
The receiver according to the related art, shown in FIG. 2, can use the sigma-delta A/D converter. However, when a received signal has a low level, a separate AGC structure is required for the sigma-delta converter to normally process a signal. This may cause an increase in manufacturing costs.
However, if the AGC structure is not used, the modulator cannot detect RSSI.